1. Field of the Invention
The present invention relates to a highly acoustic auto ceiling panel and its manufacturing process.
2. Description of the Prior Art
The conventional auto ceiling panel represents a three-layer structure of a metal lath held between two foamed polyethylene layers with isolated bubbles thermally fused thereto or a four-layer one of a metal lath held on both sides between one foamed polyethylene layer with a polyvinylchloride sheet and another foamed polyethylene layer. In such a laminated structure (of three layers or four layers), the heat insulation effect and the safety to human body may be satisfactory enough, but the interior noise insulation effect is not sufficient, because the bubbles of the foamed plastic layers in the structure are not isolated.
It is known that the acoustic performance of auto ceiling panel can be improved by providing through holes in the panel. Provision of through holes in such a structure of three or four layers, however, is hindered by the metal lath held between the foamed polyethylene layers; and this is difficult after lamination.
For these reasons, in the present practice of manufacture the through holes are bored separately in respective foamed polyethylene layers to be plastered together and thereafter these layers are laminated on both sides of the metal lath. Even in this practice, it is difficult to get a lamination with identical pattern on the top and bottom sides, resulting in that a very few holes running through both foamed polyethylene layers are obtained and thus for all the bother of working, the acoustic effect attained is not remarkable.
Related patents of applicants' are U.S. Pat. Nos. 4,128,682, 4,128,683, and 4,129,672.